Details

Description

The last correct Version was 15w40b, both 15w41b and 15w42a are affected.

The Pos-Tag of a ItemFrame, that got summoned is set to the the Position of the Player or whatever summoned the ItemFrame. That is wrong because an ItemFrame's Position is always right in front of the wall it is hanging on.
Saving and reloading the world will fix the Pos-Tag.

Shulkers are similar in the sence, that there Pos-Tag is always centered on their current block. Shulkers are not affected by this bug and work correctly.

Why is this a Problem?
The big Problem resulting from this behaviour is related to the /execute command. /execute seems to take the Pos-Tag value. This means that /execute will behave different on ItemFrames that got summoned in this session, than on ItemFrames that got summoned before the last reload.

Many advanced Redstone Systems used the fixed Pos-Tag of ItemFrames to center Marker ArmorStands on blocks. This bug makes this almost impossible.